Unlocking Insights from In-Situ Meltpool Monitoring Data for Additively Manufactured NiTi Components

This presentation explores the interconnected aspects of in-situ infrared (IR) melt-pool data analysis and its implications on residual stress, volumetric energy density (VED) influence, and the effects of aging heat treatment on the properties of NiTi materials manufactured through Powder Bed Fusion using a Laser Beam (PBF-LB). Assessment methods includes part-scale residual stress simulation, microscopy, phase analysis, nanoindentation, and the study of residual stress-induced crack morphologies.

The similarities of residual stress contours from simulation with the reconstructed 2D and 3D thermograms reconstructed from the IR melt pool data provides compelling evidence in support of the temperature gradient mechanism of residual stress formation during the PBF-LB processing of NiTi. The waveform of the IR data also indicates degree of thermal cycling.

Further IR data analyses reveals that higher VED values, determined by hatch spacing (specifically, 80 and 120 J/mm³), lead to elevated normalized mean melt layer temperatures, increased thermal gradients, heightened thermal cycling, thermally induced residual stresses, and subsequent liquation microcracks within the microstructure. Under identical aging conditions, the recrystallization and phase transformation behaviours in NiTi samples exhibit significant variations based on the PBF-LB parameters employed, primarily due to disparities in the initial thermal histories identified through post-analysis of compiled IR melt pool data.

The synergies we have identified between in-situ IR monitoring data and the resulting properties of fabricated NiTi components represent a critical step forward in advancing our understanding, and contribution to the realization of concepts like closed-loop digital twin systems, as well as the objectives of Industry 4.0.